Before lawmakers left town last month for the weeklong Memorial Day recess, Republican leaders said they would begin drafting legislation to repeal and replace Obamacare.

This week, Senate lawmakers will begin asking to see details on how Senate GOP leaders hope to write a measure that can attract at least 50 Republican votes.

"It's difficult to know what to expect," said Michael Cannon, director of health policy studies at the CATO Institute, a libertarian think tank.

It's also hard to predict when to expect a draft bill.

Senate Majority Whip John Cornyn of Texas told KFYO radio last week he was confident the Senate would pass a bill to repeal and replace Obamacare before departing for the August recess.

"Oh, absolutely, we'll get it done by the end of July at the latest," Cornyn said.

President Trump has also started applying pressure, using Twitter to nudge the Senate along.

"Hopefully Republican Senators, good people all, can quickly get together and pass a new (repeal & replace) HEALTHCARE bill. Add saved $'s," Trump tweeted last week.

Senate Republicans have for weeks been debating a healthcare bill in closed-door meetings in the Capitol. Republican senators have met three days each week in an effort to find consensus on a proposal. Separately, a working group made up of about a dozen members has been huddling twice each week to hash out an agreement.

Lawmakers said they have not come to a consensus on a plan.

Sen. Ron Johnson, R-Wis., told reporters last week that despite the lack of an agreement, Senate GOP leadership staff would work on a draft bill over the May recess.

The staff on the Health, Education, Labor and Pensions Committee is expected to play a key role in writing the draft, lawmakers said.

GOP leaders told Republicans the HELP panel "would be drafting a bill over recess," a GOP aide told the Washington Examiner. "We were not told they would be finished."

Senators have repeatedly dismissed a House-passed bill to repeal and replace Obamacare.

The House version would replace healthcare subsidies with tax credits and allow states to seek waivers for the Obamacare mandates. The legislation would create high-risk pools for the hard-to-insure.

Republican senators don't agree with much of the House bill, which, for example, does aim tax credits at low-income earners. Senate GOP Conference Chairman John Thune wants to include a means test for tax credits.

"We agree that to pass a bill in the Senate, we would have to come up with a structure that is different than the House," Thune, of South Dakota, said of the House tax credit provision.

The House bill would also leave 23 million uninsured, according to a Congressional Budget Office report, and it has polled poorly.

A Kaiser Health Tracking poll last week found 8 percent of respondents favor the Senate passing the House bill without changes. An additional 50 percent said the Senate should make minor or major changes to the House bill, while another 29 percent said the Senate should ditch the House bill completely.